共查询到20条相似文献,搜索用时 31 毫秒
1.
This paper describes different approaches to achieve high-performance microfabricated silicon-glass separation columns for microgas chromatography systems. The capillary width effect on the separation performance has been studied by characterization of 250-, 125-, 50-, and 25-$muhbox{m}$ -wide single-capillary columns (SCCs) fabricated on a $10 times 8 hbox{mm}^{2}$ die. The highest plate number (12 500/m), reported to date for MEMS-based silicon-glass columns, has been achieved by 25-$muhbox{m}$-wide columns coated by a thin layer of polydimethylsiloxane stationary phase using static coating technique. To address the low sample capacity of these narrow columns, this paper presents the first generation of MEMS-based “multicapillary” columns (MCCs) consisting of a bundle of narrow-width rectangular capillaries working in parallel. The theoretical model for the height-equivalent-to-a-theoretical-plate $(HETP)$ of rectangular MCCs has been developed, which relates the $HETP$ to the discrepancies of the widths and depths of the capillaries in the bundle. Two-, four-, and eight-capillary MCCs have been designed and fabricated to justify the separation ability of these columns. These MCCs capable of multicomponent gas separation provide a sample capacity as large as 200 ng compared to 5.5 ng for 25-$muhbox{m}$-wide SCCs.$hfillhbox{[2007-0309]}$ 相似文献
2.
Inchworm microactuators are popular in micropositioning applications for their long ranges. However, until now, they could not be considered for applications such as in vivo biomedical applications because of their high input voltages. This paper reports on the modeling, design, fabrication, and testing of a new family of pull-in-based electrostatic inchworm microactuators which provides a solution to this problem. Actuators with only 7-V operating voltage are achieved with a $pm 18hbox{-}muhbox{m}$ total range and a $pm 30hbox{-}muhbox{N}$ output force. Larger operating voltage (16 V) actuators show even better results in force ($pm 110 mu hbox{N}$) and range $(pm 35 muhbox{m})$. The actuator has an in-plane angular deflection conversion which provides a force-displacement tradeoff and allows us to set step sizes varying from few nanometers to few micrometers with a minor change in design. In this paper, we designed 1- and 4-$muhbox{m}$ step-size devices. The actuator step size may change during the operation because of the slipping of the shuttle and the beam bending; however, our model successfully explains the reasons. One of our actuator prototypes has survived more than 25 million cycles without performance deterioration. The device is fabricated using the silicon-on-insulator-based multiuser MEMS process.$hfill$[2007-0146] 相似文献
3.
The flow driven by a valveless micropump with a single cylindrical pump chamber and two diffuser/nozzle elements is studied theoretically using a 1-D model. The pump cavity is driven at an angular frequency $omega$ so that its volume oscillates with an amplitude $V_{rm m}$. The presence of diffuser/nozzle elements with pressure-drop coefficients $zeta_{+}$, $zeta_{-}( ≫ zeta_{+})$ and throat cross-sectional area $A_{1}$ creates a rectified mean flow. In the absence of frictional forces the maximum mean volume flux (with zero pressure head) is $Q_{0}$ where $Q_{0}/V_{rm m}omega = (zeta_{-} -break zeta_{+})pi/16(zeta_{-}+zeta_{+})$, while the maximum pressure that can be overcome is $Delta P_{max}$ where $ Delta P_{max}A_{1}^{2}/V_{rm m}^{2} omega^{2} !=! (zeta_{-} -break zeta_{+})/16$. These analytical results agree with numerical calculations for the coupled system of equations and compare well with the experimental results of Stemme and Stemme.$hfill$ [2008-0244] 相似文献
4.
A laterally movable gate field effect transistor (LMGFET) device that directly couples lateral mechanical gate motion to drain current of a FET is presented in this paper. Lateral motion of the FET gate results in a change in channel width, keeping the channel length and the gap between the gate and the oxide layer constant. This results in a change in channel current that, in principle, is linearly proportional to mechanical motion. The operating principle of an LMGFET, along with details of the fabrication process for a depletion-type LMGFET device, is described. Fabricated LMGFET shows an average drain current sensitivity to gate motion of $-5.8 muhbox{A}/muhbox{m}$ at $V_{rm DS} = 20 hbox{V}$ and $V_{rm GS} = 0 hbox{V}$ for 60-$muhbox{m}$ gate motion. A model for the fabricated LMGFET is developed based on electrical measurements. The device shows promise both as a sensor and as an actuator in MEMS and other related applications.$hfill$ [2008-0147] 相似文献
5.
We investigate the $ {cal L}_{2}$ gain of periodic linear switched systems under fast switching. For systems that possess a suitable notion of a time-average system, we characterize the relationship between the ${cal L}_{2}$ gain of the switched system and the ${cal L}_{2}$ gain of its induced time-average system when the switching rate is sufficiently fast. We show that the switched system ${cal L}_{2}$ gain is in general different from the average system ${cal L}_{2}$ gain if the input or output coefficient matrix switches. If only the state coefficient matrix switches, the input-output energy gain for a fixed ${cal L}_{2}$ input signal is bounded by the ${cal L}_{2}$ gain of the average system as the switching rate grows large. Additionally, for a fixed ${cal L}_{2}$ input, the maximum pointwise in time difference between the switched and average system outputs approaches zero as the switching rate grows. 相似文献
6.
This paper presents a contactless droplet manipulation system that relies on thermally generated Marangoni flows. Programmable 2-D control of aqueous microdroplets suspended in an oil film on a plain featureless glass substrate is achieved using a 128-pixel heater array suspended 100–500 $mu hbox{m}$ above the oil layer. The heaters generate surface temperature perturbations $(≪ 25 ^{circ}hbox{C})$, resulting in local Marangoni flows that can move droplets in either a push or a pull mode. Programmed movement is achieved by the sequential activation of the heaters, with digital control circuitry and a graphical interface providing addressable control of each heater. Droplets with diameters of 300–1000 $muhbox{m}$ are manipulated and merged at speeds up to 140 $muhbox{m/s}$. Evaporation rates can be reduced by almost two orders of magnitude by using a two-layer-oil medium, and the choice of an optimum carrier fluid can achieve fluid velocities over 17 000 $mu hbox{m/s}$. The system provides a contactless platform for parallel droplet-based assays. As such, it circumvents the challenges of sample contamination and loss that occur when a droplet interacts with a solid surface.$hfill$[2008-0272] 相似文献
7.
Three ways to approximate a proximity relation $R$ (i.e., a reflexive and symmetric fuzzy relation) by a $T$ -transitive one where $T$ is a continuous Archimedean $t$-norm are given. The first one aggregates the transitive closure $overline{R}$ of $R$ with a (maximal) $T$-transitive relation $B$ contained in $R$ . The second one computes the closest homotecy of $overline{R}$ or $B$ to better fit their entries with the ones of $R$. The third method uses nonlinear programming techniques to obtain the best approximation with respect to the Euclidean distance for $T$ the $Lstrok$ukasiewicz or the product $t$-norm. The previous methods do not apply for the minimum $t$-norm. An algorithm to approximate a given proximity relation by a ${rm Min}$-transitive relation (a similarity) is given in the last section of the paper. 相似文献
8.
A hybrid integrated circuit (IC)/microfluidic chip is presented that independently and simultaneously traps and moves microscopic objects suspended in fluid using both electric and magnetic fields. This hybrid chip controls the location of dielectric objects, such as living cells and drops of fluid, on a 60 $times$ 61 array of pixels that are $30 times 38 mu hbox{m}^{2}$ in size, each of which can be individually addressed with a 50-V peak-to-peak dc-to-10-MHz radio-frequency voltage. These high-voltage pixels produce electric fields above the chip's surface with a magnitude $vert vec{E}vert approx 1 hbox{V}/muhbox{m}$ , resulting in strong dielectrophoresis (DEP) forces $vert vec{F}_{ rm DEP}vert approx 1 hbox{nN}$. Underneath the array of DEP pixels, there is a magnetic matrix that consists of two perpendicular sets of 60 metal wires running across the chip. Each wire can be sourced with 120 mA to trap and move magnetically susceptible objects using magnetophoresis. The DEP pixel array and magnetic matrix can be used simultaneously to apply forces to microscopic objects, such as living cells or lipid vesicles, that are tagged with magnetic nanoparticles. The capabilities of the hybrid IC/microfluidic chip demonstrated in this paper provide important building blocks for a platform for biological and chemical applications. $hfill$[2009-0142] 相似文献
9.
This paper examines the use of deep reactive ion etching of silicon with fluorine high-density plasmas at cryogenic temperatures to produce silicon master molds for vertical microcantilever arrays used for controlling substrate stiffness for culturing living cells. The resultant profiles achieved depend on the rate of deposition and etching of an $hbox{SiO}_{x}hbox{F}_{y}$ polymer, which serves as a passivation layer on the sidewalls of the etched structures in relation to areas that have not been passivated with the polymer. We look at how optimal tuning of two parameters, the $ hbox{O}_{2}$ flow rate and the capacitively coupled plasma power, determine the etch profile. All other pertinent parameters are kept constant. We examine the etch profiles produced using electron-beam resist as the main etch mask, with holes having diameters of 750 nm, 1 $muhbox{m}$ , and 2 $muhbox{m}$. $hfill$[2008-0317] 相似文献
10.
Motivated by questions in robust control and switched linear dynamical systems, we consider the problem checking whether all convex combinations of $k$ matrices in $R^{n times n}$ are stable. In particular, we are interested whether there exist algorithms which can solve this problem in time polynomial in $n$ and $k$. We show that if $k= lceil n^{d} rceil $ for any fixed real $d>0$, then the problem is NP-hard, meaning that no polynomial-time algorithm in $n$ exists provided that $P ne NP$, a widely believed conjecture in computer science. On the other hand, when $k$ is a constant independent of $n$ , then it is known that the problem may be solved in polynomial time in $n$. Using these results and the method of measurable switching rules, we prove our main statement: verifying the absolute asymptotic stability of a continuous-time switched linear system with more than $n^{d}$ matrices $A_{i} in R^{n times n}$ satisfying $0 succeq A_{i} + A_{i}^{T}$ is NP-hard. 相似文献
11.
We have developed a MEMS probe-card technology for wafer-level testing ICs with 1-D line-arrayed or 2-D area-arrayed dense pads layouts. With a novel metal MEMS fabrication technique, an area-arrayed tip matrix is realized with an ultradense tip pitch of $90 muhbox{m} times 196 mu hbox{m}$ for testing 2-D pad layout, and a 50-$muhbox{m}$ minimum pitch is also achieved in line-arrayed probe cards for testing line-on-center or line-on-perimeter wafers. By using the anisotropic etching properties of single-crystalline silicon, novel oblique concave cavities are formed as electroplating moulds for the area-arrayed microprobes. With the micromachined cavity moulds, the probes are firstly electroplated in a silicon wafer and further flip-chip packaged onto a low-temperature cofired ceramic board for signal feeding to an automatic testing equipment. The microprobes can be efficiently released using a silicon-loss technique with a lateral underneath etching. The measured material properties of the electroplated nickel and the Sn–Ag solder bump are promising for IC testing applications. Mechanical tests have verified that the microprobes can withstand a 65-mN probing force, while the tip displacement is 25 $muhbox{m}$, and can reliably work for more than 100 000 touchdowns. The electric test shows that the probe array can provide a low contact resistance of below 1 $Omega$, while the current leakage is only 150 pA at 3.3 V for adjacent probes.$hfill$[2008-0273] 相似文献
12.
This paper describes the design, microfabrication, and testing of a novel polycrystalline-diamond (poly-C)-based microprobe for possible applications in neural prosthesis. The probe utilizes undoped poly-C with a resistivity on the order of $10^{5} Omegacdothbox{cm}$ as a supporting material, which has a Young's modulus in the range of 400–1000 GPa and is biocompatible. Boron-doped poly-C with a resistivity on the order of $10^{-3} Omegacdot hbox{cm}$ is used as an electrode material, which provides a chemically stable surface for both chemical and electrical detections in neural studies. The probe has eight poly-C electrode sites with diameters ranging from 2 to 150 $muhbox{m}$; the electrode capacitance is approximately 87 $muhbox{F/cm}^{2}$. The measured water potential window of the poly-C electrode spans across negative and positive electrode potentials and typically has a total value of 2.2 V in 1 M KCl. The smallest detectable concentration of norepinephrine (a neurotransmitter) was on the order of 10 nM. The poly-C probe has also been successfully implanted in the auditory cortex area of a guinea pig brain for in vivo neural studies. The recorded signal amplitude was 30–40 $muhbox{V}$ and had a duration of 1 ms. $hfill$[2008-0195] 相似文献
13.
We present a new temperature compensation system for microresonator-based frequency references. It consists of a phase-locked loop (PLL) whose inputs are derived from two microresonators with different temperature coefficients of frequency. The resonators are suspended within an encapsulated cavity and are heated to a constant temperature by the PLL controller, thereby achieving active temperature compensation. We show repeated real-time measurements of three 1.2-MHz prototypes that achieve a frequency stability of $pm$ 1 ppm from $-20 ^{circ}hbox{C}$ to $+80 ^{circ}hbox{C}$, as well as a technique to reduce steady-state frequency errors to $pm$0.05 ppm using multipoint calibration.$hfill$[2009-0074] 相似文献
14.
A 30-mm-long multimode waveguide, 40 $muhbox{m}$ wide and 40 $muhbox{m}$ high, is fabricated on a silicon wafer using polymer SU-8 as the core and liquid buffer as the cladding. Antibodies are successfully immobilized on the SU-8 surface designated for binding target antigens dispersed in the buffer solution. Evanescent-wave spectroscopy is performed by exciting the fluorescently labeled antigens, bound to the waveguide surface within its evanescence field, and measuring the emission light intensity. This evanescent-wave biosensor detects specific molecular interaction. The optical output as a function of the antigen concentration can be described by Langmuir equation. Antigen concentration as low as 1.5 $muhbox{g}/hbox{mL}$ is detected; concentrations higher than 100 $muhbox{g}/hbox{mL}$ lead to sensor saturation. $hfill$[2008-0058] 相似文献
15.
Two versions of microdischarge-based pressure sensors, which operate by measuring the change, with pressure, in the spatial current distribution of pulsed dc microdischarges, are reported. The inherently high temperatures of the ions and electrons in the microdischarges make these devices amenable to high-temperature operation. The first sensor type uses 3-D arrays of horizontal bulk metal electrodes embedded in quartz substrates with electrode diameters of 1–2 mm and 50–100-$muhbox{m}$ interelectrode spacing. These devices were operated in nitrogen over a range of 10–2000 torr, at temperatures as high as 1000 $^{circ}hbox{C}$. The maximum measured sensitivity was 5420 ppm/torr at the low end of the dynamic range and 500 ppm/torr at the high end, while the temperature coefficient of sensitivity ranged from $-$925 to $-$550 ppm/K. Sensors of the second type use planar electrodes and have active areas as small as 0.13 $hbox{mm}^{2}$. These devices, when tested in a chemical sensing system flowing helium as a carrier gas, had a maximum sensitivity of 9800 ppm/torr, a dynamic range of 25–200 torr, and a temperature coefficient of sensitivity of approximately $-$1412 ppm/K.$hfill$ [2008-0262] 相似文献
16.
N-channel 6H-SiC depletion-mode junction field-effect transistors (JFETs) have been fabricated, and characterized for use in high-temperature differential sensing. Electrical characteristics of the JFETs have been measured and are in good agreement with predictions of an abrupt-junction long-channel JFET model. The electrical characteristics were measured across a 2-in wafer for temperatures from 25 $^{ circ}hbox{C}$ to 450 $^{circ}hbox{C}$, and the extracted pinchoff voltage has a mean of 11.3 V and a standard deviation of about 1.0 V at room temperature, whereas pinchoff current has a mean of 0.41 mA with standard deviation of about 0.1 mA. The change in pinchoff voltage is minimal across the measured temperature range, whereas pinchoff current at 450 $^{circ}hbox{C}$ is about half its value at room temperature, consistent with the expected change in the $nmu_{n}$ product. The characterization of differential pairs and hybrid amplifiers constructed using these differential pairs is also reported. A three-stage amplifier with passive loads has a differential voltage gain of 50 dB, and a unity-gain frequency of 200 kHz at 450 $^{circ}hbox{C}$, limited by test parasitics. A two-stage amplifier with active loads has reduced sensitivity to off-chip parasitics and exhibits a differential voltage gain of 69 dB with a unity-gain frequency of 1.3 MHz at 450 $^{circ}hbox{C}$.$hfill$[2009-0029] 相似文献
17.
A high-sensitivity capacitive humidity sensor intended for use as part of a respirator end-of-service-life indicator system is presented. This paper reports a method for improving the sensitivity of integrated capacitive chemical sensors by removing the underlying substrate. The sensor is integrated with CMOS testing electronics using maskless postprocessing followed by ink-jet deposition of a sensitive polymer. Two different methods of depositing polymer, namely, capillary wicking and coating the top surface directly, were investigated. The sensors had measured sensitivities of 0.16% to 0.18% change in capacitance per percent relative humidity, which is the highest demonstrated for an integrated capacitive humidity sensor. Temperature sensitivity of the sensor, which is an important criterion for a sensor intended for a variety of different ambient conditions, was measured to be $0.07%/^{circ}hbox{C}$. The cross sensitivities to toluene and acetone, which are two common industrial solvents that are filtered by respirator cartridges, were measured to be $2.4 times 10^{-4}$ and $9.0 times 10^{-5}%/hbox{ppm}$, respectively.$hfill$ [2009-0165] 相似文献
18.
This paper presents the design, fabrication, and characterization of a new serial digital actuator, achieving an improvement in range-to-precision and range-to-voltage performance. We propose a weight-balanced design for the serial actuators with serpentine springs with a serial arrangement of unit digital actuators. We have measured the displacement range, precision, and drive voltage of unit and serial actuation at 1 Hz. The serial digital actuators produce a full-range displacement of $28.44 pm 0.02 muhbox{m}$ , accumulating unit displacements of $2.8 pm 0.5 muhbox{m}$ at an operating voltage of 4.47 $pm$ 0.07 V. In addition, the serial digital actuators that have a displacement precision of 37.94 $pm$ 6.26 nm do not accumulate the displacement errors of the unit actuators, i.e., 36.0 $pm$ 17.7 nm. We experimentally verify that the serial digital actuators achieve a range-to-squared-voltage ratio of 1.423 $muhbox{m/V}^{2}$ and a range-to-precision ratio of 749.6.$hfill$ [2009-0020] 相似文献
19.
Field-effect control of electroosmotic (EO) flow, which has been demonstrated on single microchannels, provides a novel method to modulate the zeta potential and, therefore, the EO flow through a porous membrane. To realize field-effect control of EO pumping with a membrane, a $hbox{SiN}_{rm x}$-coated porous silicon membrane was designed and fabricated. The heavily doped silicon core was used as a conducting electrode to apply the transverse gate potential, which modulates the zeta potential of the channel walls and, thereby, the EO flow rate with constant externally applied electric fields along the channels. We observed significant electrolytic-rectification effect, i.e., for gate voltage $(V_{g}) ≪ 0$, a substantial current leakage through the $ hbox{SiN}_{rm x}$ was observed, whereas negligible leakage current was detected for $V_{g} ≫ 0$. Significant EO flow control, nearly 70% reduction in flow velocity, was observed for positive gate bias, while only 15% flow-velocity enhancement was observed for negative gate bias of similar magnitude. This first demonstration of field-effect control on porous membranes opens the door for making high-flow rate EO pumps with porous membranes of low zeta potential materials. $hfill$[2009-0048] 相似文献
20.
A microelectromechanical system actuator based on thermophoretic, or Knudson, forces is proposed using analytical calculations. It can potentially execute scanning or spinning motions of a body that is not mechanically attached to the reference substrate. For a silicon device of 100-$muhbox{m}$ diameter, it is calculated that it can be levitated at a distance of about 0.5 $muhbox{m}$ from a substrate and that it can execute scanning motion and use quasi-springs by laterally acting thermal forces. In this way, an engine with spinning motion of a floating body having a diameter of 200 $muhbox{m}$ with up to 5 kHz can be achieved.$hfill$[2008-0013] 相似文献
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